What gobies are you looking at? Some are territorial. I have a 12usg nano cube. I have a fire fish and may add a blue spot jawfish and that's it.
I love blue spot jawfish. I got a mated pair of yellow heads, but oh, are those blue spots gorgeous! I shall covet it when you get one.
Yeah, some gobies are territorial. This is for an approximate 8g? I've got a yellow watchman in mine with a tiger pistol. Other people keep the high-fin banded gobies and the Yashas with randal's pistol shrimp. These fish jump, though, so a tight lid is needed. No gaps. Fire fish are nice too, but jumpers as well. My new 8g will feature a Helfrich's fire fish and another fish of some type. I'm mulling it over. A lot of choices if you're creative. The key, IMO, is to pick two fish of contrasting habits and who occupy very different zones of the tank. They shouldn't look similar either.
L